Parramatta ended the wait to replace sacked Brad Arthur with an early-morning announcement on Monday, following last week's board meeting.
Ryles' appointment means he has beaten Queensland and Cronulla assistant Josh Hannay for the job, while Dean Young and interim coach Trent Barrett were the other main contenders.
Jason Ryles beat Maroons assistant Josh Hannay (right) to the Eels job. (Darren England/AAP PHOTOS)
Ryles has long been viewed as an NRL coach in waiting, having helped win the 2016 and 2020 premierships as an assistant to Craig Bellamy at the Storm.
His resume also boasts stints as Trent Robinson's right-hand man at the Sydney Roosters and with England's rugby union team under Eddie Jones.
"We are delighted to welcome Jason to the Parramatta Eels," Eels chairman Sean McElduff said.
"Jason's proven track record in winning environments, combined with his passion for developing young talent perfectly aligns with the direction we are taking our club.
"We have a strong NRL roster and a group of exciting young players coming through our pathways programs.
"We believe Jason is the ideal person to build a strong connection within the playing group, across the club and with the passionate Parramatta Eels fanbase."
Jason Ryles previously worked as an assistant to Trent Robinson at the Roosters. (Mark Evans/AAP PHOTOS)
Ryles will see out the season in Melbourne, before joining Parramatta after this year's finals.
His first challenge will be retaining the core members of Parramatta's squad, with star five-eighth Dylan Brown holding an option in his contract to leave at the end of 2025.
Arthur's links to the mooted Perth NRL expansion team could compound the challenge, given members of the Eels playing group remain close to their long-serving former coach, who was axed in May.
On-field results are also in need of big improvement; Parramatta has conceded more points (470) than any other team through 18 rounds to slump to 16th place on the ladder.
"I am incredibly honoured to be appointed head coach of the Parramatta Eels," Ryles said.
"This is a club with a rich history and a passionate fanbase. I look forward to coaching these young men."
Ryles' appointment will also raise questions over who will eventually replace Bellamy in Melbourne, where the veteran coach is on a year-by-year arrangement.
Ryles had long been considered Bellamy's successor, most recently turning down St George Illawarra's head coaching job in 2023 to return to the Storm as an assistant.
But the Storm will now likely need to look elsewhere when the master coach calls it quits; premiership-winning player Ryan Hinchcliffe, Marc Brentnall, and Bellamy's son Aaron are currently on staff as assistants.
Billy Slater has often been floated as a potential heir given his long-standing connection with the club and burgeoning coaching career with Queensland in Origin.
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